Various mobile and stationary machine systems use conveyors for moving bulk materials from place to place. Different types of conveyors are known, such as belt conveyors including endless canvas, rubber or metal belts which support the material being moved and are pulled over pulleys or rollers, chain or cable conveyors which include chains or cables adapted to pull plates, buckets or containers loaded or filled with material being moved, and auger or screw conveyors which include a helix formed about a turning shaft for moving material through a tube.
Mobile machine systems which use conveyors include various types of agricultural vehicles and construction equipment. Combines, for example, typically include a clean grain elevator for moving material up to a delivery auger, a delivery auger for moving the clean grain into the grain bin, a tailings auger for moving tailings to the tailings elevator to be returned to the threshing system of the combine, and an unloading auger for moving material from the grain bin to a transport device. Other examples include cotton pickers having a conveyor for moving cotton into storage bins, planters having a conveyor for moving seeds or fertilizer, and forage harvesters having a conveyor to move foraged material. Some conveyors include pneumatic delivery systems which are used, for example, to deliver seed from a seed bin to a planter or to convey forage from a forage harvester to a wagon. Stationary systems using conveyors include, for example, grain elevators using a conveyor including a driven chain which pulls paddles loaded with grain.
The machine systems described above may include real-time sensors and systems for measuring or monitoring parameters of material moved by the conveyors. These sensed parameters may include, for example, the yield or mass flow rate of material being moved by the conveyor, or the moisture content of the material. For example, yield and moisture sensors may be mounted to a grain auger of a combine to measure the mass flow rate and moisture content of grain flowing through the auger.
Known systems for measuring moisture may include capacitive sensors mounted in or on a fin which extends into the flow of material to measure the capacitance of the material. These systems extend into the flow of material so that the sensors can detect moisture despite their limited range. However, the intrusion into the flow of materials may cause certain materials, such as plant residue or sap, to build up on the sensors as contact is made with material being moved. The resulting build-up can cause the sensors to give inaccurate or erroneous readings. In addition, the intrusion of the sensors into the material may restrict or interrupt the flow of material, and the exposed fins and sensors are subject to mechanical wear and breakage.
Other measuring systems use capacitive sensors in a test cell which receives a small portion of the material flow diverted from the main flow. Such systems, however, require additional components and structures to divert the flow of material from the main flow and for the test cell, thereby increasing cost and decreasing reliability. Such systems may also suffer from build-up on the sensors since the material makes contact with the sensors.
Known sensors used to measure certain parameters of material being moved, such as yield or mass flow rate, may contain radioactive isotopes. These sensors may be subject to regulation concerning their sale and use since they are radioactive sources, thereby subjecting the user to the increased costs and paperwork associated with regulation compliance. The user is also exposed to the costs and risks generally associated with the use and management of radioactive sources. Other yield sensors generate signals when harvested grain hits a plate, the signals depending on both the amount of grain hitting the plate and the force at which the grain hits. These sensors may be inappropriate for measuring parameters of certain non-granular materials, such as forage, and may be difficult to integrate into a particular system.
Another problem with known systems for measuring parameters of a material includes the limited frequency response of such systems. Certain parameters of a material, such as type, mass flow rate, moisture content, density or other parameters, can be identified or measured by driving a sensing element with different frequencies and measuring the response of the material to each frequency. For example, one measuring system which uses a capacitive sensor in a test cell includes three fixed frequency generators which generate three fixed frequency signals and a multiplexer which sequentially applies the frequency signals to the sensor. The response at each frequency is then measured. This system, however, may be unable to provide required resolution over a given frequency range because of the fixed frequency signals. Moreover, expansion of this system to include a sufficient number of frequency generators to provide the required resolution over a given frequency range may be impractical because of the high number of frequency generators needed. Another measuring system includes a sweeping frequency oscillator which drives a capaciflector sensor. This latter system is able to generate more frequencies than the former system. However, when a dynamic system is being measured, the use of swept frequencies may introduce errors because the dynamic system may change over the time required to sweep the frequency signals.